Procedures for preparing photographic images in silver by diffusion transfer principles are well known in the art. For the formation of the positive silver image a latent image contained in an exposed photosensitive silver halide emulsion is developed and almost concurrently therewith a soluble silver complex is obtained by reaction of a silver halide solvent with the unexposed and the undeveloped silver halide of said emulsion. Preferably, the photosensitive silver halide emulsion is developed with a processing composition in a viscous condition which is spread between the photosensitive element comprising the silver halide emulsion and a print receiving element comprising a suitable silver precipitating layer. The processing composition effects development of the latent image in the emulsion and substantially contemporaneous therewith forms a soluble silver complex, for example, a thiosulfate or thiocyanate complex, with undeveloped silver halide. This soluble silver complex is, at least in part, transported in the direction of the print receiving element and the silver ion thereof is largely reduced to silver metal and precipitated in the silver precipitating element to form a positive image thereon. Procedures of this type are disclosed, for example, in U.S. Pat. No. 2,543,181 issued to Edwin H. Land. See also Edwin H. Land; One Step Photography; Photographic Journal, Section A, pages 7-15, January, 1950.
Additive color reproduction may be obtained by exposing a photosensitive silver halide emulsion through an additive color screen having filter media or screen elements each of an individual additive color such as red, or green, or blue, and by viewing the reversed or positive silver image formed by transfer to a transparent print-receiving element through the same or a similar screen which is suitably registered with the reversed positive image carried by the print-receiving layer.
As examples of suitable film structures for employment in additive color photography mention may be made of the U.S. Pat. Nos. 2,861,885, 2,726,154, 2,944,894, 3,536,488, 3,615,427, 3,615,428, 3,615,429, 3,615,426, and 3,894,871.
U.S. Pat. No. 3,364,482 discloses an additive color diffusion transfer film unit of the type described above which comprises, in order, a support, an additive color screen, silver precipitating nuclei in a processing composition permeable layer, a non-nucleating photoinsensitive layer, and a silver halide emulsion layer. The aforementioned non-nucleating photoinsensitive layer is preferably deacetylated chitin whose primary purpose is to provide a protective barrier over the nucleating layer which, subsequent to exposure and processing, contains the positive silver image, after the silver halide emulsion layer has been detached from the remainder of the film unit.
A novel and improved additive color diffusion transfer film unit has now been found.